Snap action electrical switch



Jan. 30, 1962 G, LEUPOLD 3,019,312

SNAP ACTION ELECTRICAL SWITCH Filed Sept. 5, 1959 INVENTOI".

fiery 6. 02400 BY fi United States Patent 3,019,312 SNAP ACTION ELECTRICAL SWITCH Henry G. Leupold, Arlington, Mass, assignor to United Eleetric Controls Company, Watertown, Mass, a corporation of Massachusetts Filed Sept. 3, 1959, Ser. No. 837,974 8 Claims. (Cl. 200-67) This invention pertains to electrical switches of the snap action type and more especially to improvements in the type of switch illustrated and described in the patent to Frederick J. Broch, No. 2,729,715, dated January 3, 1956.

Such switches employ an unstable spring and linkage mechanism constrained so that a free end of the spring can move only a relatively short distance in either direction from the balanced position. In operation, a pivot is moved until the system is unbalanced in a direction in which motion is possible. The free end of the spring then suddenly snaps in that direction and remains in that position until the pivot is moved into the complementary un-' balanced position.

In the Broch switch the movable pivot and the linkage are combined in a tensioning element consisting of a piece of thin flexible sheet metal of generally rectangular contour having a large elongate central opening thereby defining a pair of transversely narrow, generally parallel arms connected at their ends by transverse web portions. One of the transverse webs includes hinge means for attachment to the free end of the spring and the other such web is secured to the switch case.

The switch also comprises an externally accessible movable part as, for example, an axially movable pin and means for transmitting the motion of the pin to the arms of the tensioning element.

In a snap switch of this type it is desirable that the switch contacts be placed ofiE-center so as to obtain the greatest possible length for the tensioning element in a case of standard dimensions. The movable contact is accordingly attached to one side of the tensioning element and located between vertically spaced fixed contacts attached t0 the base of the switch. In such an arrangement, where the contacts are located unsymmetrically, there is a tendency for the tensioning element to warp slightly due to the normal pressure of the movable contact against the upper fixed contact, and thus one arm of the tensioning element may normally be higher than the other. If the actuating force is then applied to the arms by a transverse element rigidly connected to the operating pin, some of the work energy available to operate the switch may be wasted in restoring the tensioning element to a horizontal plane, thus causing a loss of sensitivity.

A further objection to having the operating force applied to the arms by a transverse element rigidly connected to the operating pin is that, in order to preserve the point of contact between the transverse element and the arms of the tensioning element, it is necessary to prevent any rotation of the operating pin. The Broch patent proposes to accomplish this, either by making the operating pin of non-circular cross-section or by providing the transverse element with laterally projecting lugs for engagement with vertical grooves in the inner surface of the side walls of the cover. Both of these methods are expensive and both have a tendency to cause binding in the travel of the operating pin.

Accordingly, objects of the present invention are to provide means for distributing an operating force equally between the two arms of the tensioning element without regard to their relative vertical disposition or to any inequality in their deflections as the force is applied and to render determinate and invarying the point of application of the operating force to the arms of the tensioning 3,919,312 Patented Jan. 30, 1952 element without requiring that the operating pin be restrained r'rom rotation.

Further objects of the present invention are to provide a switch of extreme sensitivity which will incorporate a force-transmitting mechanism of simple and inexpensive construction including an operating pin of circular crosssection.

According to the present invention the operating pin bears pivotally upon a transverse force-transmitting member which, in turn, bears pivotally upon the arms of the tensioning element. In a transverse plane, this forcetransmitting element acts as a beam balance, distributing the force applied by the operating pin to each of the arms of the tensioning element equally. By the nature of this balancing action the forces applied to the two arms are equal despite any relative vertical displacement and despite any inequality in the deflections of the arms as the force is applied.

In the preferred embodiment the transverse force-transmitting and distributing element is not attached either to the actuating pin or to the arms of the tensioning element, but is loosely connected to the body of the switch only, at a point spaced somewhat from the actuating pin, and is free to pivot and tilt transversely about this point except as restrained laterally by the sides of the cover to the switch and as restrained vertically by the arms of the tensioning element below and the actuating pin above.

For the purpose of illustration, a typical embodiment the invention is shown in the accompanying drawings in which:

FIG. 1 is a side elevation;

FIG. 2 is a plan view with the cover removed and with parts broken away.

FIG. 3 is a side elevation with the cover in vertical section;

FIG. 4 is a fragmentary vertical section through the cover, showing a modification of the actuating pin;

FIG. 5 is a plan view of the transverse balancing ele ment;

FIG. 6 is a plan view of the tensioning element to smaller scale than FIG. 2;

FIG. 7 is a section on the line 7-7 of FIG. 6;

FIG. 8 is a section, to larger scale, on the line 8-8 of FIG. 3; and

FIG. 9 is a fragmentary transverse section, to larger scale, showing, in exaggerated position, the force-transmitting member and the arms of the tensioning element.

Referring to the drawings, and particularly FIGS. 1-3, the base 1 of the switch consists of a generally rectangular substantially rigid block of an appropriate dielectric moldable material such as Bakelite, its external dimensions preferably being those which have become a standard for snap switches of this general type, for instance, of a length of 1 a width of and a depth, with cover, of with the axis of the actuating pin at a distance of approximately /2 from one end.

At the right-hand end of the base, as viewed in FIGS. 2 and 3, are two vertically spaced contacts 2 and 3, the upper contact 2 being supported directly above the lower contact 3 by bracket means 4.

An abutment 5, carried by the base, has at its righthand end, a V-shaped groove for receiving the stationary end 6a of the compression spring 6. The left-hand end of the abutment has an opening therethrough for a screw 7 whereby the abutment is secured to the base 1.

The tensioning element E (FIGS. 3 and 6) consists of a piece of very flexible sheet material, for example copper-beryllium alloy of the order of 0.006 inch in thickness, of generally rectangular shape having a large elongate central opening thereby defining a pair of spaced, generally parallel arms 9 connected at their ends by transverse web portions 11 and 12 (FIG. 6). The left-hand web portion 11 has an opening therethrough for the screw '7; and underlies the end of the abutment furthest from the compression spring, and is thereby clamped to the base 1. The right-hand web portions 12 carries a movable contact 13 interposed between the fixed cont acts 2 and 3. A hinge means 14 for receiving the movable end of the compression spring 6, is also carried by the right-hand web 11 at a point spaced from the contact 13.

Intermediate the ends of the tension element 8, but nearer to clamped web 11 than to the hinge means 14, each arm 9 has an integral downwardly directed elongate flange 15 at right angles to the arm proper, these flanges stiffening that part of the tensioning element to which the operating force is applied.

The cover 16 of the switch has a cylindrical guide bore for the actuating pin 13. The axis of the actuating pin is substantially vertical. Desirably the lower end of the guide here is flared and the head 13a of the pin is correspondingly beveled, so that in the idle position the head of the pin occupies but little space within the casing and is not cramped between the inner surface of the casing and the balancing element upon which it rests. The convex head 18a of the pin 18 bears freely and pivotally upon the transverse balancing element 19 (FIG. 5) which in turn rests upon dimples 2i (FIGS. 6 and 8) struck up from the arms of the tensioning element E.

While in the preferred embodiment depicted, the upstanding dimples Ztl on the arms 9 of the tensioning element are shown as being directly opposite one another, it is to be understood that they may be shifted laterally with respect to each other or to the operating pin so as to compensate for any otherwise unbalanced forces existing in the switch without departing from the essential spirit of the present invention. The transverse balancing or force-distributing element 19, as here illustrated comprises a generally triangularly shaped, rigid, fiat piece of dielectric material, one corner of which has an opening through which loosely passes a screw 21 (FIGS. 2 and 3) by which the element 19 is connected to the base 1 of the switch. The same screw 21 also secures the cover 16 to the base.

As suggested in FIG. 9, the attachment of the transverse balancing element 19 to the base 1 is loose enough to allow said element to tilt freely in the transverse direction, that is to sa about an axis which is parallel to the length of the tensioning element, thereby to adapt itself to any ditference in the relative heights of the arms of the tensioning element, whereby force, applied to the actuating pin 18, will be distributed equally and simultaneously to both of the arms 7.

The transverse balancing element 19 is restrained from moving unduly, in the lateral direction, by the side walls 22 of the cover 16.

In the modification shown in FIG. 4 the hole in the cover for the reception of the operating pin 26a is made airtight by a flexible seal 27.

For convenience in description reference has been made to the right and left-hand ends of the switch base and of certain parts of the switch, but it is to be understood that these terms are only used with reference to the accompanying drawing and are not to be considered as in any way limiting the position in which the switch may be used.

It should also be understood that this disclosure is for the purpose of illustration only and that this invention includes all modifications andequivalents which fall within the scope of the appended claims.

I claim:

1. In a snap action electrical switch of the kind which comprises a rigid base and a removable cover, both of insulating material, opposed vertically spaced fixed contacts adjacent to one end of the base, a compression spring, a normally fixed abutment for one end of the compression spring, a tensioning element comprising a pair of narrow, generally parallel arms connected at their ends by transverse webs, means fixing one of said webs to said base, hinge means connecting that end of the tensioning element which is remote from the fixed web to the free end of the compression spring, a movable contact interposed between said fixed contacts, means for transmitting motion from the free end of the compression spring to said movable contact, and an actuating pin, in combination, means operative to distribute operative force, applied to the actuating pin, equally bett can the arms of the tensioning element without regard to their relative vertical disposition.

2. A switch as in claim 1 wherein the means for distributing operative force equally between the arms of the tensioning element comprises a rigid balancing element which is freely tiltable about an axis parallel to the length of the tensioning element, and wherein the lower end of the actuating pin contacts the balancing element at a point intermediate the lateral edges of the latter, and the actuating pin is free to rotate around its own axis.

3. A switch as in claim 1 wherein the means for distributing operative force equally between the arms of the tensioning element comprise a rigid balancing element which is freely tiltable about an axis parallel to the length of the tensioning element, and wherein the arms of the tcnsioning element have upstanding projections upon which the balancing element bears.

4. A switch as in claim 3 wherein the means for distributing operative force equally between the arms of the tensioning element comprises a rigid balancing element which is freely tiltable about an axis parallel to the length of the tensioning element, and wherein the upstanding projections on the arms of the tensioning elements are dimples struck up from the material of the tensioning element and integral therewith.

5. A switch as in claim 3 wherein the means for distributing operative force equally between the arms of the tensioning element comprises a rigid balancing element which is freely tiltable about an axis parallel to the length of the tensioning element, and wherein the balancing element is connected to the base only and is free to move relatively to the base except as restrained laterally .by the side walls of the cover and vertically by the actuating pin above and the arms of the tensioning element below.

6. A switch as in claim 3 wherein the means for distributing operative force equally between the arms the tensioning element comprises a rigid balancing element which is freely tiltable about an axis parallel to the length of the tensioning element, and wherein the balancing element comprises a flat piece of insulating material'iof a generally triangular shape and has an aperture near one corner, and a screw, passing loosely through said aper-v ture, connects the balancing element to the base, said screw fastening the cover to the base.

7. A snap action electrical switch of the kind which comprises a base, a compression spring, a normally fixed abutment for one end of the compression spring,'a tensioning element comprising a pair of narrow, generally parallel arms connected at their ends 'by transverse webs, means fixing one of said webs to said base, hinge means connecting that end of the tensioning element, which is remote from the fixed web, to the free end of the compression spring, and an actuating pin, in combination, means operative to distribute operative force, applied to the actuating pin, equally between the arms of the tensioning element without regard to their relative dispositions, the tensioning element having integral, transversely spaced, upstanding projections to which actuating force is applied by the distributing means.

8. A snap action electrical switch of the kind which comprises a compression spring, the movable end of References Cited in the file of this patent UNITED STATES PATENTS Bugge June 13, 1950 Mosley Oct. 14, 1952 Broch Jan. 3, 1956 Harrold Oct. 30, 1956 Cunningham Sept. 30, 1958 FOREIGN PATENTS Sweden July 27, 1948 

